1. Field of the Invention
Embodiments of the present invention generally relate to methods and apparatus for completing a well. Particularly, embodiments of the present invention relate to hydraulic tools which may be used to set a liner top packer and/or may be used to resist the lifting forces of cementing pack-offs.
2. Description of the Related Art
In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling a predetermined depth, the drill string and bit are removed and the wellbore is lined with a string of casing. An annular area is thus formed between the string of casing and the formation. A cementing operation is then conducted in order to fill the annular area with cement. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
It is common to employ more than one string of casing in a wellbore. In this respect, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The first string of casing is hung from the surface, and then cement is circulated into the annulus behind the casing. The well is then drilled to a second designated depth, and a second string of casing, or liner, is run into the well. The second string is set at a depth such that the upper portion of the second string of casing overlaps with the lower portion of the upper string of casing. The second “liner” string is then fixed or “hung” off of the upper surface casing. Afterwards, the liner is also cemented. This process is typically repeated with additional liner strings until the well has been drilled to total depth. In this manner, wells are typically formed with two or more strings of casing of an ever-decreasing diameter.
The process of hanging a liner off of a string of surface casing or other upper casing string involves the use of a liner hanger. The liner hanger is typically run into the wellbore above the liner string itself. The liner hanger is actuated once the liner is positioned at the appropriate depth within the wellbore. The liner hanger is typically set through actuation of slips which ride outwardly on cones in order to frictionally engage the surrounding string of casing. The liner hanger operates to suspend the liner from the casing string. However, it does not provide a fluid seal between the liner and the casing. Accordingly, it is desirable in many wellbore completions to also provide a packer.
During the wellbore completion process, the packer is typically run into the wellbore above the liner hanger. A threaded connection typically connects the bottom of the packer to the top of the liner hanger. Known packers employ a mechanical or hydraulic force in order to expand a packing element outwardly from the body of the packer into the annular region defined between the packer and the surrounding casing string. In addition, a cone is driven behind a tapered slip to force the slip into the surrounding casing wall and to prevent packer movement. Numerous arrangements have been derived in order to accomplish these results.
A problem associated with conventional mechanically actuated packer systems is the potential that the mechanical force applied to the packer may insufficiently set the packer resulting in a liner overlap without the desired pressure integrity. For example, in deviated or horizontal wellbores, the friction between the landing string and the wellbore limits the amount of mechanical force that can be applied to set the packer. Thus, this limited mechanical force may be insufficient to set or fully set the packer.
Hydraulically actuated packers can be set with the more consistent force of hydraulic pressure. A problem associated with conventional hydraulically actuated packers is that the landing string and running tools oftentimes must remain tied onto the liner for the packer to be actuated. Staying tied onto the liner during cementing operations increases the risk of having cement around the landing string and running tools without being able to release from the liner.
Another problem associated with conventional hydraulically actuated packers is that the packers may prematurely set. For example, some conventional hydraulically actuated packers are actuated by applying a hydraulic pressure to shear the shearable device to release the packer actuating sleeve/polished bore receptacle, or other actuator device. Thus, if a hydraulic pressure is increased over the force required to overcome the shearable device, the packer can prematurely set.
Another problem encountered when installing liners is that during the cementing of liners the hydraulic pressure of the cement acts on the cementing pack-off and urges the cementing pack-off upward. Sufficient downward force must be applied to the running tool assembly to resist the cementing pack-off from being lifted out of sealing engagement with the liner or the cementing pack-off must be mechanically locked to the liner to resist movement. In deviated or horizontal wellbores, the amount of force that can be applied to resist this lifting force may be limited by the friction between the landing string and the wellbore. A problem with mechanically locked cementing pack-offs is that the cementing pack-off may become stuck and may be difficult to be released from the liner.
Therefore, there is a need for an improved device and method for setting liner top packers. In addition, there is a need for an improved device for resisting the lifting forces of cementing pack-offs.